Rootstock is usually used for grafting.  People buy rootstock and graft the varieties they want to the rootstock.
Dolgo is becoming popular with some folks as a rootstock for apple grafting.  If it is true Dolgo it would make a Dolgo tree without grafting, and that would be okay if you want Dolgo.  Bartlett is a fireblight magnet.  I don't want a Bartlett Pear and I don't want Bartlett rootstock for grafting.  It might be okay for grafting, but I personally don't want it after the research I've done on how rootstock can affect disease resistance.